1. Field of the Invention
The present invention generally relates to the field of vehicular wheelchair lifts for persons who are physically challenged or otherwise have limited mobility. More particularly, the present invention relates to the field of hydraulic powered wheelchair lifts with automatically foldable platforms.
2. Description of the Prior Art
Vehicular wheelchair lifts are widely utilized to assist persons in wheelchairs to get in and out of vehicles. These lifts typically have a mobile platform for transporting an occupied wheelchair, where the platform can be raised and lowered between a loading position at the ground level outside a vehicle and an entry position at the floor level inside the vehicle. When not in use, the platform can be stored inside the vehicle.
U.S. Pat. No. 4,140,230 issued to Pearson on Feb. 20, 1979 discloses a powered loading platform. The platform is pivotally supported by a support means which is in turn carried by a powered parallelogram linkage. The parallelogram linkage is driven by an electric motor through a gear system. The platform is formed by two grates which are hingeably connected so that one grate can be folded over and stacked on the other grate for storage purposes. One disadvantage of this platform is that it is powered by an electrical motor which is severely limited by the vehicle's electrical power source. Another disadvantage of this platform is that the folding and stowing of the platform each require a separate manual operation.
U.S. Pat. No. 5,401,135 issued to Stoen et al. on Mar. 28, 1995 discloses a foldable platform wheelchair lift with safety barrier. The wheelchair lift in general includes a main frame and a support frame which is pivotally connected to the main frame. The support frame supports a platform and can be moved through a parallelogram linkage. The platform consists of two half-sections which can be folded when not in use. The lift utilizes a barrier mechanism which functions as a safety stop for preventing the wheelchair from inadvertently rolling off of the platform. The lift further utilizes a latching mechanism for coupling the folded platform when it is in the stowed condition. Again, one of the disadvantages of this lift is that the folding and stowing of the platform still each require a separate manual operation.
U.S. Pat. No. 4,534,450 issued on Aug. 13, 1985 to Savaria (hereafter referred to as "the '450 Patent"), who is also the inventor of the present invention, discloses a vehicular wheelchair lift with a powered platform. The platform is supported by a support frame which can be raised or lowered by a hydraulically powered parallelogram linkage. The platform consists of two independent half-sections displaceable between a coplanar position and a transverse position. When the platform is pivoting to an upstanding position, the two independent half-sections are also caused to pivot from their coplanar position to the transverse position through respective tie-rod assemblies. This feature eliminates the separate manual operation for folding and stowing the platform. When the wheelchair lift is in its stored condition, the two independent half-sections of the platform rest in an upright orientation on the two opposite sides of a vehicle door and are cleared out of the passageway of the vehicle door.
While the wheelchair lift disclosed in the '450 Patent provides certain advantages such as a powerful single hydraulic pump as the power source and the automatic folding of the split platform, it is desirable to further design and develop a wheelchair lift which has a compact stowing profile and folds only on one side of the vehicle door, which leaves more room inside the vehicle and is also more suitable for smaller vehicles with narrower doors. It is also desirable to provide a vehicular wheelchair lift which has a simplified construction but is strong, safe, reliable, durable and cost effective, and still possess the advantageous features such as the single hydraulic power source and automatic folding and stowing of the platform.